Apparatus for the production of polyphase gypsum

ABSTRACT

Gypsum is treated in a final burning cyclone which discharges into a conveyor which is arranged to feed to a discharge into a cooling line leading to a cooling cyclone. The cooling line is connected to a humidifier and may be operated with or without the humidifier. Material is also fed to the conveyor from a material bin located downstream of the final burning cyclone. A bypass is connected to the conveyor to feed directly from the discharge of the final burning cyclone into the cooling line. With the inventive method, polyphase gypsum with an adjustable setting behavior is produced by first heating gypsum to form a phase mixture of dihydrate, hemihydrate and anhydrites. The heating is carried out in a carrier gas burning plant with a burning gas temperature which is only slightly above the exit terminature of the burnt material and part of the anhydrite III, which is undesired in the end product, is then rehydrated to hemihydrate. The rehydration of anhydrite III is effected by introducing the phase mixture into a cooling air current having an absolute humidity which can be regulated to about 30 g/Nm3 depending on the portion of the anhydrite III.

United States Patent [191 Jenne et al.

[ Aug. 13, 1974 APPARATUS FOR THE PRODUCTION OF POLYPHASE GYPSUM [75] Inventors: Oswald Jenne; Josef Steinkuhl, both of, Essen; Otto Wiechmann, Recklinghausen; Gerhard Reimann,

Mulheim, all of Germany [73] Assignee: Rheinstahl AG, Essen, Germany [22] Filed: Oct. 16, 1972 '21 App]. No.: 298,009

' [30] Foreign Application Priority Data Primary Examiner.lohn J. Camby Attorney, Agent, or Firm-John J. McGlew ABSTRACT Gypsum is treated in a final burning cyclone which discharges into a conveyor which is arranged to feed to a discharge into a cooling line leading to a cooling cyclone. The cooling line is connected to a humidifier and may be operated with or without the humidifier. Material is also fed to the conveyor from a material bin located downstream of the final burning cyclone. A bypass is connected to the conveyor to feed directly from the discharge of the final burning cyclone into the cooling line. With the inventive method, polyphase gypsum with an adjustable setting behavior is produced by first heating gypsum to form a phase mixture of dihydrate, hemihydrate and anhydrites. The heating is carried out in a carrier gas burning plant with a burning gas temperature which is only slightly above the exit terminature of the burnt material and part of the anhydrite III, which is undesired in the end product, is then rehydrated to hemihydrate. The rehydration of anhydrite III is effected by introducing the phase mixture into a cooling air current having an absolute humidity which can be regulated to about 30 g/Nm3 depending on the portion of the anhydrite III.

4 Claims, 1 Drawing Figure APPARATUS FOR- THE PRODUCTION OF POLYPHASE GYPSUM BACKGROUND OF THE INVENTION 1. Field of the Invention This invention relates in general to a method and apparatus for treating gypsum and, in particular, to a new and useful method and apparatus for the production of polyphase gypsums which comprises anhydrites, hemihydrate and dihydrate with an adjustable setting behavior, for example, with a setting start of between 4 to 25 minutes and with a setting end from between 10 to 120 minutes.

2. Description of the Prior Art A known method of burning polyphase gypsum is carried out in a gas-burning plant, preferably with several series-connected cyclones, and the temperature of the entering heating gas current is regulated so that it is only slightly above the exit temperature of the burnt material, particularly 1.1 to 2 times higher, and the stay period of the material in the heating gas current is regulated to the range of from 0.5 to 10 seconds and the relative humidity of the heating gas current relative to the operating temperatures maintain to an amount of from 40 to 95 percent. The raw material has a grain size of up to 2mm, with a preferred grain size of from to 400 1.1.. With this method, it is possible to produce the various gypsum phases and modifications in one and the same plant and in a continuous operation, with the phases being separated from each other or regulated in a desired mixture as polyphase gypsum. In respect to the production of the polyphase gypsum, particularly plaster, which consists for example, of 42 percent anhydrite II, 13 percent anhydrite Ill, 33 percent hemihydrate, 2 percent dihydrate and percent inert substance, and also in the production of individual phases and modifications, it was found necessary to constantly supervise the composition both of the end product and the products of the individual treatment stages. This supervision is always advisable for fixed quantities, such as temperatures, grain sizes, etc., inasmuch as the starting product frequently has a varying water content so that displacements of the portions of the individual phases and modifications may result in an end product which has differing properties.

In a still unpublished report, there is a suggestion that the content of crystal water as an identification mark for the presence of the various phases can be used for the supervision of the composition of the product from the various phases and modifications and for the control of the process for the production of gypsum of a certain composition. The existence of the various phases, namely, anhydrite, hemihydrate and dihydrate may be determined by the crystal water content of the material issuing from the individual cyclone stages and by controlling the measured value of the portions of the total burned material flowing through the individual.

states in order to form the final composition of the end product.

In an older method for the production of gypsum with several phases, for example, wall and floor plaster, and wherein there is a rotary chamber or furnace, a certain composition of the product is achieved by a socalled double burning where a part of the gypsum rock is burnt at high temperatures to anhydrite which is mixed while still hot with the other crushed part of the gypsum rock. The crushed gypsum rock is burnt by the heat of the anhydrite to he'mihydrate which is required for the mixing phase.

It was found in practice that polyphase gypsums show relatively great variations intheir setting behavior even with careful supervision of the production process and this is obviously due to the metastable phases, particularly the metastable highly hygroscopic anhydrite Ill, undergoes substantially atransformation during storage by absorbing moisture from the air, in this case, to semihydrate. Since this process, called aging, depends to a great extend on the humidity, the temperature of the surrounding atmosphere and the time, this may lead to unforeseeable fluctuations in the setting behavior of the polyphase gypsum.

SUMMARY OF THE INVENTION In accordance with the present invention, the shortcomings of the prior art in the manufacture of polyphase gypsums are overcome, and a method and apparatus is provided for the production of polyphase gypsums by which a very uniform and constant setting start and setting end may be obtained'and also particularly good physical properties of the resulting gypsum. The invention provides a carrier gas burning method which permits the accurate production of polyphase gypsums of certain composition. With the inventive method, a phase mixture of dihydrate, hemihydrate and anhydrite is produced in a carrier gas burning plant with a burning gas temperature which is only slightly above the :exit temperature of the burnt material and that part of the anhydrite III which is undesired in the end product is rehydrated to hemihydrate.

According to one embodiment of the invention, the rehydration of anhydrite III is effected by introducing the phase mixture into a cooling air current having an absolute humidity which can be regulated in dependence upon the portion of the anhydrite III :up to about 30 g/Nm.

In accordance with another embodiment of the invention, the rehydration of anhydrite III is effected by intensive admixture of fine grained dihydrate or dihydrate-containing substances to the phase mixture in such an amount that the water released .from the dihydrate corresponds to the 1.1 to 1.4 fold stoichometric amount which is necessary to 'rehydrate anhydrite III'to hemihydrate.

A particularly favorable embodiment of the invention comprises the rehydration of the :anh-ydrite III by adding to the phase mixture fine-grained dihydrate or dihydrate-containing substances and introducing the entire mixture into a wet or dry cooling .air current.

Another favorable embodiment -.of the invention comprises the rehydration of anhydrite lI'I byadding to apart of the phase mixture fine grained dihydrate -.or dihydrate-containing substances :while the other part is introduced simultaneously into a cooling air current with regulated humidity.

The metastable anhydrite III, which is formed .in large quantities of up to 30 percent in the high-temperature burning of the gypsum, is converted by rehydration Lto vhemihydrate except for a small amount which is desired in the end product since it has a great stimulating effect on the beginning stiffening. The other-wise unavoidable spontaneous conversion of anhydrite III is thus :no longer left to the accidental and slow action of "the humidity on the finished product. Rather, a finished stable end product is provided by the shock-like rehydration, whose setting behavior is not subject to fluctuations.

It was found that polygypsums treated in this way show surprisingly a much greater strength than other polyphase gypsums, which is obviously due to the fact that the dihydrate, which is formed after the setting from the hemihydrate formed by the rehydration of anhydrite III, shows a particularly favorable crystal form.

The apparatus for carrying out the method comprises I a mixing and conveying device arranged at the discharge of the burning cyclone and which opens into a discharge at its extreme end which leads to a cooling cyclone line. In addition, a material discharge is connected into the conveyor downstream of the high temperature connection for dosing an amount of ground dihydrate or dihydrate-containing substances into the conveyor and mixing device. The cooling line contains an adjustable air humidifier. The material discharge of the cooling cyclone advantageously opens into a suction pipe leading to another cooling cyclone which can also be connected to a humidifier.

Accordingly, it is an object of the invention to provide a method for producing polyphase gypsums of uniform characteristics and setting behavior.

A further object of the invention is to provide a method for producing polyphase gypsums with an adjustable setting behavior wherein a phase mixture of dihydrate, hemihydrate and anhydrites is produced in a carrier gas burning plant with a burning gas temperature which is only slightly above the exit temperature of the burnt material and part of the anhydrite III which is undesired in the end product is then rehydrated to hemihydrate.

A further object of the invention is to provide a polyphase gypsum by effecting the rehydration of anhydrite III by adding to the phase mixture fine grained dihydrate or dihydrate-containing substances and introducing the entire mixture into a wet or dry cooling air current.

A further method of the invention is to produce a polyphase gypsum by effecting the rehydration of anhydrite III by introducing the phase mixture into a cooling air current whose absolute humidity can be regulated depending on the portion of anhydrite III to about 30 g/Nm A further object of the invention is to provide an apparatus for producing polyphase gypsum which comprises at least one heating cyclone having a heating material discharge and which is heated by heating gases which are generated in a combustion device and transmitted to the cyclone and which includes a conveyor connected between the discharge of the cyclone to a cooling conduit and a separate storage bin for feeding additional material to the conveyor downstream of the high temperature heating cyclone and with a bypass for the high temperature heating cyclone for feeding the material directly into the cooling conduit.

A further object ,of the invention is to provide a method and apparatus for forming polyphase gypsum which is simple in design, rugged in construction and economical to manufacture.

For an understanding of the principles of the invention, reference is made to the following description of a typical embodiment thereof as illustrated in the accompanying drawing.

BRIEF DESCRIPTION OF THE DRAWING The only FIGURE of the drawing is a schematic elevational view of a plant for manufacturing gypsum constructed in accordance with the invention.

GENERAL DESCRIPTION OF THE PREFERRED EMBODIMENT Referring to the drawing in particular, the invention embodied therein comprises a finish burning cyclone 1 of a carrier gas burning plant into which heating gas is sucked by a fan (not shown) from a separate combustion device 2. The finish burning cyclone 1 is charged from a preburning cyclone 4 having a discharge 4a regulated by a valve 41) which discharges into an inlet connection M for the finish burning cyclone 1. Heating gases are connected through a conduit 22 back to the preburning cyclone 4 where they are employed for the preburning operation and then passed through a discharge 24. Fine grained material (a dihydrate) is delivered to a bin 3, which has a discharge 3a, with a branch connection 3b connected to the return gas conduit 22 and a downpipe 7 which discharges downwardly.

In accordance with the invention, a combined mixing and conveying device 6, for example in the form of a screw conveyor, is connected at its inlet end to a discharge connection 5 from the final burning cyclone 1 and it is provided with a discharge at its opposite end connected into a downwardly extending discharge 26 which leads into a cooling conduit or duct 10. The downpipe 7from the bin 3 also connects into the combination mixing and conveying device 6 between the discharge 5 and the discharge 26. Fine grained raw material (dihydrate and dihydrate-containing substances) can be added in adjustable amounts to the phase mixture produced in the carrier gas burning plants and discharged from the final burning cyclone 1 through the discharge 5. Suitable valves 28 in the downpipes 7 and 30 in the bypass 3b are provided for controlling the amount of the additions and recycling of the material.

The cooling duct 10 is subjected to a suction produced by a fan 9 which connects to a cooling cyclone 8. An adjustable humidifier 11 is also connected to the opposite end of the line 10. In the arrangement shown, the material is intentionally wetted in the line 10 and cooled by the intake air. In accordance with a feature of the invention, an adjustable bypass 21 interconnects the inlet end of the mixing and conveying device 6 with the cooling conduit 10 in order to provide for a feed directly from the discharge 5 of the final burning cyclone 1 into the cooling conduit.

The cooling cyclone 10 includes a discharge 12 which connects into a second cooling line 14 which is under the action of the suction fan 9 and which also connects to a second cooling cyclone 13. This second cooling conduit 14 can be regulated by a regulating valve 15 so that it may be connected either to atmosphere or the humidifier 11 as desired. The cooling air which is circulated into cyclones 8 and 13 are fed through lines 15 and 16 respectively after they provide their cooling function and are delivered into a dust separator 17 which, for example, can be a cloth filter. The material which is in the cooling cyclone 13 is fed through a discharge 13a to a delivery conduit 19 along with material which is separated in the dust separator 17 which passes through the'discharge 18 into the conduit 19. The delivery conduit 19 delivers the material into the finished goods bins, generally designated 20.

The apparatus, according to the invention, can be operated so that the material issuing from the discharge 5 arrives in the cooling line without any admixture of dihydrate or dihydrate-containing substances merely by bypassing the combination mixing and conveying device 6 and delivering the material through the bypass 21 directly into the cooling conduit 10. In such an instance, the material is then fed directly into the cooling conduit and through the cooling cyclones 8 and 13 and the anydraite III in rehydrated to hemihydrate by the humidity of the cooling air while the material is cooled at the same time. If necessary, the cooling conduit 13 can be operated with dry cooling air by disconnecting the humidifier.

In accordance with another method of operation of the apparatus, the amount of dihydrate or dihydratecontaining substances necessary for the rehydration of anhydrite III is added through the line 7 to the material which is moved in the combination mixing and conveying device 6. This mixture is then treated in the cooling conduit 10 and the cyclones 8 and 13 with humid air or dry air and, at the same time, it becomes cooled. It is possible to cool with dry air in the two cyclones 8 and 13 and, in such an instance, the humidifier 11 is shut down. The humidifier l1 advantageously includes an inlet 11a for air, a water spray 11b and a water receiving trough 110.

A still further method of operation is possible by directing only a part of the material which arrives through the discharge 5 into the combined mixing and conveying device 6 through the bypass 21 directly into the cooling air line 10 and delivering a further part through the discharge 26 at the opposite end of the conveyor. In this manner, an amount of dihydrate or dihydrate-containing substances necessary for the rehydration of anhydrite III is added through the line 7 to the part of the mixture which is delivered through the discharge 26.

When the plant is operated, the treated material is delivered to the bin ready for use and this is unlike the finished product produced according to the conventional methods. The material delivered is always uniform and will exhibit very little change in composition and setting power during the complete operation of the plant. In addition, the material is cooled to a temperature which permits immediate packing into bags.

While a specific embodiment of the invention has been shown and described in detail to illustrate'the application of the principles of the invention, it will be understood that the invention may be embodied otherwise without departing from such principles.

What is claimed is:

1. An apparatus for producing polyphase gypsum, comprising at least one heating cyclone having a vertically extending heated material discharge pipe, means for supplying heating gases to said cyclone, a raw material storage bin for fine grained dihydrate material having a vertically extending dihydrate material discharge pipe extending substantially parallel to and spaced from said heated material discharge, a cooling conduit, a conveyor arranged below said heated material discharge pipe and solid dihydrate material discharge pipe and connected to said heated material discharge and to said fine grained material discharge at spaced locations in series and having a final discharge connected into said cooling conduit.

2. An apparatus for producing polyphase gypsum, according to claim 1, including a bypass connected to said heated material discharge and connecting directly into said cooling conduit.

3. An apparatus for producing polyphase gypsum, according to claim 1, including a first cooling cyclone connected to said cooling conduit and having a first cooling cyclone discharge, a second cooling cyclone connected to the discharge of said first cooling cyclone, a humidifier having-an inlet for air connected to said cooling conduit and having a connection to said second cooling cyclone, and adjustable means in the connection to said second cooling cyclone for connecting and disconnecting said second cooling cyclone to the humidifier and to atmosphere.

4. An apparatus for producing polyphase gypsum, according to claim 3, wherein said first and second cooling cyclones have connections to a dust separator, the material treated in said first cooling cyclone being delivered to said second cooling cyclone, said second cooling cyclone discharging into a delivery conduit which is also connected to said dust separator. 

1. An apparatus for producing polyphase gypsum, comprising at least one heating cyclone having a vertically extending heated material discharge pipe, means for supplying heating gases to said cyclone, a raw material storage bin for fine grained dihydrate material having a vertically extending dihydrate material discharge pipe extending substantially parallel to and spaced from said heated material discharge, a cooling conduit, a conveyor arranged below said heated material discharge pipe and solid dihydrate material discharge pipe and connected to said heated material discharge and to said fine grained material discharge at spaced locations in series and having a final discharge connected into said cooling conduit.
 2. An apparatus for producing polyphase gypsum, according to claim 1, including a bypass connected to said heated material discharge and connecting directly into said cooling conduit.
 3. An apparatus for producing polyphase gypsum, according to claim 1, including a first cooling cyclone connected to said cooling conduit and having a first cooling cyclone discharge, a second cooling cyclone connected to the discharge of said first cooling cyclone, a humidifier having an inlet for air connected to said cooling conduit and having a connection to said second cooling cyclone, and adjustable means in the connection to said second cooling cyclone for connecting and disconnecting said second cooling cyclone to the humidifier and to atmosphere.
 4. An apparatus for producing polyphase gypsum, according to claim 3, wherein said first and second cooling cyclones have connections to a dust separator, the material treated in said first cooling cyclone being delivered to said second cooling cyclone, said second cooling cyclone discharging into a delivery conduit which is also connected to said dust separator. 